Vibratory system



April 28, 1925.

J. P. MAXFIELD ET AL VIBRATORY SYSTEM Filed Jail, 5, 1925 l um Amp/wrmedos@ Hen Patented Apr. 28, 1,925. 'I

1,535,538 UNITED STATES PATENT OFFICE.

JOSEPH 1. MAXFIELD, OF MAPLEWOOD, NEW JERSEY, AND `HENRY C. HARRISON, OFPORT WASHINGTON, NEW YORK, ASSIGNORS TO WFSTERN ELECTRIC COMPANY,INCORPORATEE'OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

VIBRATORY SYSTEM.

` Application-ined January s, 192s. serial No. 610,537.

To 11,15 whom 'it'may concern Be it known that we, JOSEPH P. MAXFIELDand HENRY C. HARRISON, citizens of the United States, residino' atMaplewood, in

5 lthe county of Essex, tate of New Jersey, and at Port Washington, inthe county of Nassau, State of New York, res ectively, have invented newand useful mprovements in -Vibratory Systems, of which the following isa full, clear, concise, and exact description.

This invention relates to vibratory systems and more 'particularlyrelates to mechanical vibrating systems which are Y electrically driven.

One Obect of thel inventionis to reduce ldis'tortionin a vibratorysystem.

y Another object is to provide means and methods for damping themechanical vibration of a moving system.

The forms of this invention hereinafter described, illustrate howdistortion, due to natural resonance effects in various types ofvibrating systems, may be avoided by a suitable damping mechanism. Brifly, the damping mechanism providesmeans for producing electrically,a'force proportional to but 180 out of phase withthe velocity of themoving system. The generated electromotive force may either be fed backupon the electric circuit producing the vibration'y (if the'movingsystem, or may be made to react by a separate mechanism upon the movingsystem, with, ofcourse, a force 180 out of phase with the velocity ofVibration. Amplifiers of the vacuum tube type, for example, may beutilized in amplifying the electromotive force in controllable amounts,and suitable adjustable phase-shifting networks may be employed.- forinsuring that there is a 1809 phase shift for as wide av frequency bandas is desired.l Referring to the drawings, Fig. 1. discloses thisinvention applied tothe damping of an Voscillograph suspension. ,Figa12v is a modification of Fig. 1; Figs-3` shows this invention jappliedto the damping of anv electromagnetic receiver; -Figj'tillustrates how acarv-bon'button may bev employed for damping an electromagneticreceiver; Fig. 5 illustrates how a variable capacity' may be employed tofurnish the electromotlve force for damping a vibratory system; Fig. 6

type of phonograph recorder; Fig. 7 is another modification of Fig. 1 asapplied to an oscillograph suspension; and Fig. 8 shows how a telephonetransmitter may be damped in accordance with this invention.

Referring to Fig. 1, an incoming 'line 9 is disclosed in which it isassumed electric vcurrents are presentv which are to be amplified by asuitable amplifier 10 and impressed upon an oscillograph suspension 11whereby the usual beam of light reflected bythe mirror 12 will bedeected in the well-known manner in accordance with the 4incomingcurrents.

4are unduly emphasized and transients are produced. The arrangementshown in Fig. 1 illustrates one way .in which this invention may beemployed for damping the oscillations of the Oseillograph whereby thisresonating effect is Vsubstantially avoided.

Line 9 is connected in series with the oscillograph suspension 11,through a. resistance 13, which forreasons given later,

should have a resistance approximately equal to the resistance of thesuspension 11. Terminal 14L of the suspension is connected to thecathode, and terminal 15 to the control electrode of a vacuum tubeamplier 16, while that terminal of resistance 13 adjacent theoscillograph is connected to the cont-rol electrode, and the otherterminal of theresistance 13 to the cathode of a second vacuum tubeamplifier 17. The anode 18 vof tube 16 is connected to the cathode'by a,circuit includin a source of volta 19 and a resistance 20, while anode21 o tube 17 is connected to its cathode by `a; circuit including asource of voltage 22 and a resistance 23. Assuming that tubes 16 and 17are identical with respect to impedance andV operating characteristics,resistances 20 and 23 should be of equal values. The-outside terminalsvof'resistances 20 and 23 are connected through a phase shifting networkcomprising nductances 24, 25 and 26,v

illustrates this invention applied to one condenser-s 27 and 28 andleads 29 and 30,

back to the line 9 between the amplifier 10 and the oscillograph. l

With the apparatus connected as above described, the control electrodeof tube 16 will have impressed thereon a potential having twocomponents, one proportional tothe velocity of the suspension 11, due tothe fact that the oscillograph suspension 11 is vibrating in a magneticfield therefore produces an E. M. F. proportional to its velocity andthe second proportional to the resistance drop in the oscillograph loop.This potential due to the first component impressed on the controlelectrode of tube 16 will produce a variation in the space currentflowing through resistance 20 andv this variation in the potential dropacross the terminals of resistance 20, after being shifted 1n phase,will be impressed back on circuit 9 by means of leads 29 and 30. Thiscurrent will be proportional to the velocity of vibration of theoscillograph loop. The inductances 24,

25 and 26 and condensers 27 and 28 should be adjusted to produce such achange in the phase of the potentials amplied by tube 16 that they arefed back upon circuit 9, 180o out of phase with the potentials incircuit 9 which produced the original vibration of the suspension 11.Leads 29 land 30 will therefore feed back upon the oscillographsuspension, current proportional to, but 180 out of phase with thevelocity of suspension 11, and a damping of the vibration of thesuspension will consequently result. This, of course, will substantiallyreduce, if not entirely eliminate, the resonance effect of thesuspension for certain frequencies, since when the vfrequencies near theresonance point are impressed thereon thereby tending to produce anabnormal deflection of the oscillograph, currents proportional to, but180 out of phase with the abnormal deflection will be fed back by leads29 and 30 so that the oscillograph is prevented from overemphasizing theresonating frequencies.

In some cases it will be desirable top prevent the feed-back circuitfrom being directly responsive toI the electric potentials impressed onthe oscillograph, the so-called second component mentioned above. Asshown in Fig. 1, resistance 13 being equal to the resistance ofoscillograph 11, the control electrode of tube 16, for example,- will bemade positive with respect to its cathode due to the currents in line 9,an amount numerically equal to the potential diiference which makescontrol electrode of tube 17 negative with 'respect to its cathode. A

similar observation of course would apply d when the potentials in line9 were of such a character as to make the control electrode of tube 16negative and that of tube 17 positive. Making the control electrode oftube 16 positive will increase the current in resistance 20, and makingthe potential on the quen cy range.

control electrode of tube 17 negative will decrease the current flowthrough resistance 23. Since tubes 16 and 17 are identical andresistances 20 and 23'y are equal, it follows that the potentialdifference developed across the terminals of resistance 20 will be equaland opposite of the potential developed across the terminals ofresistance 23, so that the original electric potentials in line 9vimpressed upon tubes 16 and 17 will not be fed back by leads 29 and 30,due to the balanced relations of tubes 16 and 17. This balancedrelation, however, does not interfere with the feeding-back into thecircuit 9 of amplified potentials proportional to the potentialsdeveloped by the vibration of the suspension 1l in the usual magneticeld.

The phase shifting network comprising series adjustable inductances 24,25 and 26 and shunt adjustable condensers 27' and 28 is merelyillustrative of one form, the phase shifting network may have, and it is-to be understood that various types of phase shifting networks may beemployed as is well-known in the art for producing a desired phasedisplacement over a desired fre- A network of a plurality of recurringsections such as shown in Fig. 1, will be found particularly useful whenit is desired to produce the same phase shift over a wide frequencyrange, for example, the range of frequencies of importance in speech.

It is to be understood, of course, that the amount of amplificationproduced by tube 16 depends upon the amount of damping desired, and theamplification, of course, may be readily adjusted to give highamplification for high damping, or low amplification for low damping.The amplifier may furthermore be adjusted to give eitherunderc'ompensation or over-compensation in' addition to an exactcompensation.

Fig. 2 is a modification of Fig. 1, and is similar thereto, in that theincoming line 32 is assumed to contain electric currents' which are tobe impressed upon an oscillograph suspension 33. Line 32 is connected tothe oscillograph lthrough a transformer 34, and a resistance 35 isconnected in series with the-line and the primary winding of transformer34. vThe terminals 36 and 37 of a suitable phase shifting network 38have impressed thereon potentials proportional to the IR drop insuspension 33, and in resistance 35. As transformer 34 may be designedto give a phase shift of 180 for the potentials present-in line 32, theIR rop in suspension 33, due to these potentials will be equal andopposite in phase to the IR drop in resistance 35, providing resistance35 is of the same value as .the resistance of suspension 33. A vacuumtube amplifier 39, which is coupled to the phase shifter through asuitable input transformer 40 `shifter 38 and the amplifier 39 may beadjusted so thatv leads 41 and 42 will impress back oncircuit 32potentials proportional to yand in phase with the velocity of thesuspension. This fed-back potential will then be elpmged 180 in phase bytransformer -34 and cause the damping of the vibration of the suspensionin the manner described above.

Fig. 3 illustrates an electro-magnetic receiver having a diaphragm' 45attached to a pivoted armature 46 suitably located between the poles ofmagnet 47. The armature 46 is surrounded by coils 48 'and 49 which .areconnected to an incoming circuit 50, a telephone circuit, for example,and incoming currents from line 50 will therefore cause the armature 46to vibrate, thereby producing the vibration of the diaphragm 45, wherebythe currents present in line 50 are translated into sound waves. Inorder to prevent the .diaphragm 45 from over emphasizing frequencies\\inline 50 which are at or near the resnating frequency of the diaphragm,the damping mechanism of this invention is provided. 'lhe reed 51, whichserves to connect armature 46 to the diaphragm 45 is employed as anarmature for the electromagnet 52, whereby the moving of the reed 51towards and away from the poles of the electromagnet 52, ca uses avariable current to be produced in the coil 53 surrounding theelectromagnet and these variable currents, by a transformer 54, lnay beimpressed upon a suitable amplifier and phase shifter 55, whereby thevariable currents are amplified4 to the desired amount and shifted inphase to such an extent that the variable currents Aimpressed bytransformer 56.upon line 50 produce forces proportional to, but 180 outoi' phase with the velocity of the diaphragm 45. The telephone diaphragm45 will therefore be damped, an amount depending upon the amplificationof the variable currents developed by coil 53. Diaphragm 45 maytherefore be made to have a substantially constant response over a widerange of frequencies, for example, the range of frequency of importancein speech and music.

It is particularly advantageous to employ vacuum tubes in connectionwith this invention since tubes of the type disclosed are unidirectionaldevices and for example will not permit the potentials in line 50 fromactuating armature 51 through the electromagnet 52.

Fig. 4 is similar to Fig. 3, in that a telephone receiver is disclosed,having va diaphragm 60 connected to a pivoted armature 61, which isoscillated in accordance with currents present in an incoming line 62.The reed 63, however, which serves to conneet the armature61 to thediaphragm 60 is attached to a diaphragm 64 of a carbon buttoln 65,whereby the vibration of the reed 63 varies the pressure exerted-on thecarbon granules in a well known manner, thereby producing variations-inthe current` fiowing therethrough due to its battery 66. The amplifierand phase shifter 67 will therefore receiverpotentials proportional tothe vibration of reed 63 and consequently the amplifier and phaseshifter may be suitably adjusted to impress upon line 62 currents whichwill produce forces proportional to but 180 out of phase with thevelocity of diaphragm 60, whereby the diaphragm 60 may be made to have asubstantially constant response over a wide frequency range Fig. 5 issimilar to Fig. 4 in that an electromagnetic receiver is disclosed, Vandthe reed 70 which connects the pivoted armature vto the diaphragm 71 issuitably attached tov the movable plate 72 of a condenser transmitter73. The two terminals ot" condenser 73 are charged by a battery 74 andconse. quently the vibration of the movable plate 72 will producepotentials which may be amplified and shifted in phase by a device 75 tosuch an extent that the diaphragm 71 has a substantially constantresponse over a wide frequency range.

Y This invention, of course. is not limited to the electrical damping oftelephone receivers and oscillographs, but may be applied to Vothertypesof mechanically vibratorysystems. In Fig. 6, for example, is shownone way in which a phonograpbic recorder may be damped in accordancewith this invention. The incoming line 80 is connected in. circuit. withtwo electric coils 81 and 82` which surround a pivotedarmature 83, andis adapted to oscillate between the poles of eleetromagnet- 84. One, endof the pivoted armatiue 83 may be suitably terminated by a. phonographneedle 85, which may be employed, for example, in cutting a sound record,corresponding to the signals or messages present in line 80. Thewinding 86 of the electromagnet is energized by a suitable source ofvoltage 87. Member S8 is an auxiliary armature carried b v the armature83 of the vibrating system. and is so placed between the poles of theelectronxagnet 84, fo modulate the inductance of the magnetizing coil86, as to neither influence nor be influenced appreciably b v thealternating cnrif' rents from line 80 which drive the vibrating 88 willcause variable potentials to be'im- All) pressed upon the amplifier andphase shifter S9, which arrangement may be adjusted so that potentialswill' be impressed on line 80 which will produce forces proportlonal to,but 180o out of phase with the velocity of the vibrating system wherebythe desired damping of the vibrating system` may be produced andresonating effects ehmmated.

l".ig.-7 is a modification of Fig. 2, operatingr in a similar manner fordamping the vibration of the oseillograph suspension 90, with theexception that the amplifier employed for amplifying the currentsgenerated by the oscillograph, is the same amphfier as is employed foramplifying the orlglnal currents. A telephone transmitter 91 is shown,the currents from which are impressed upon a suitable amplifier 92,through a potentiometer 93 and by a transformer 94 upon theoscillograph. The potentials generated by the oscillograph are shiftedy1n phase by the phase shifter 95 and impressed upon an adjustableportion of the potentiometer 93 included between leads 96 and 9?,whereby the currents fed back Will be amphfied to the desired degree byamplifier 92.

The operation of the system in other respects is the same as in Fig. 2.Resistance 98 should, of course, be equal to the reslstance of theoscillograph suspension 90.

F ig. 8 discloses how this invention may be applied to produce theelectrical dampmg of a telephone transmitter. A telephone transmitterdiaphragm 99 is disclosed, which bv a member 100 is suitably connectedto a carbon button 101 to vary the pressure eX- erted on the carbongranules in the same manner as in the well known type of micro` phonetransmitter whereby the sound waves impressed upon the diaphragm 99 willbe translated into electriccurrents in line 102. ln o-rder to insurethat the response of the telephone diaphragm 99 will be substantiallyconstant over a wide frequency range, a small armature 103 is attachedto one side of the diaphragm 99 opposite the poles of an clectromagnet104. rl`he coils surrounding the electromagnct 104 are connected to theinput terminals of a vacuum tube ampllier 105, the output terminals ofwhich, through a'suitable phase shifter 106 are conuected to an electriccoil 107 of an electromagnet 108 for which the diaphragm 99 constitutesan armature. The Vvibration of the. diaphragm 99, due to impressed soundwaves, will therefore cause the variable potentials developed in thecoils of magnet 104 to be impressed upon amplifier 105, and thesevariable potentials, after amplification, may be suitably shifted inphase by the phase shifter until the force exerted by the coil 107 onthe diaphragm is proportionate to, but 180 out of phase with thevibration of the diaphragm caused bythe impressed sound waves. Themicrophone transmitter, may therefore be damped to correct for anyunequal response, the transmitter may have for impressed sound waves ofvarious frequencies.

It is to be understood that this invention is of wide application, andis capable of embodiments widely different from those described indetail above, Without departing in anywise from the spirit of thisinvention as' defined in the appended claims.

What is claimed is:

1. A mechanical vibratory system, subjected to a force for vibratingsaid system, means for producing electrically a force proport'onal tothe velocity of said system, and phase controlling means for causingsaid force to control the movement of said vibratory system.V

2. In a mechanical vibratory system subjected to a force for vibratingsaid system, means for producing an eletromotive force proportional tothe velocity, means for shifting the phase of said electromotive force,and means for causing said phase shifted electr-emotive force to producea mechanical force which damps the vibrations of the mechanical system.

8. In a mechanical vibratory" system subjected to a force forvibratingsaid system, means for producing an electromotive forceproportional to the velocity of the vibratfons of said system and meansfor causing the electromotive force to produce a force which isapproximately 180 out of phase with the velocity of the vibrating systemto damp the Vibrations of said system, said last named means comprsingunidirectional conducting and phase shifting means.

4. A mechanical vibratory system subjected to a force for vibrating saidsystem, means for producing an elect'romotive force proportional to thevelocity of the vibrations of said system, means for amplifying theelectromotive force produced. means for shifting the phase of theamplified electromotive force, and means for causing the amplified andphase-shifted electromotive force to produce a mechanical force which isapproximately 180o out of phase with the velocity of the vibratingsystem and which thereby danlps the vibrations of said system.4

5. A mechanical vibratory system having a natural period Within thevoice frcquency range, an electric circuit, means for causingthecurrents in said circuit to produce-corresponding vibrations of saidsystem, and means for damping said mechanica-l system, said dampingmeans comprising means for producing electrical current proportional to,but ap roximately out of phase with the ve ocity of said mechanicalsystem, and means for impressing said produced current upon said circuitwhereby the said produced current opposes the action of sa1d electriccurrents on said sysp tem.

' as to oppose the original currents producing the vibration of saidarmature.

7. In combination, a magnet, a pivoted armature for said magnet, a coilsurrounding said armature, an electric circuit connected to said coil,means for producing current variations proportional to the vibrations ofsaid armature, a uni-directional de vice for amplifying said variations,and means for impressing said amplified current variations upon saidcircuit inv such a manner that the force produced by the impressedcurrents is approximately 180 out of phase with the velocity of saidarmature.

8. In combination, a magnet, a pivoted armature 'for said magnet,l acoil surrounding said armature, l,an electric circuit connected to saidcoil, an electromagnet having its p ole pieces cooperating with saidarmature, an energizing winding surrounding said electromagnet, a sourceof volta e connected to said winding, .a vacuum tu e amplier, having itsinput terminals res onsive to the current variations produce in saidwinding by the vibration of said arma-v ture, connections between tleloutput terminals of said amplifier and said circuit, and means forcausing the currents received by said circuit from said amplifier `toproduce a force on said armature approximately 180 out of phase with thevelocity of said armature.

9. A mechanical vibratory system, an electric circuit, means forcausing-the current in said circuit to produce corresponding vibrationsof said system and means fordamping said mechanical syste1n,vsaiddamping means comprising means for producing an electrical currentproportional to the velocity of said mechanical system, phase shiftingmeans and unidirectional conducting means for impressing said producedcurrent upon said circuit whereby said produced current opposes theaction of said first mentioned e ectrical current on said system.

10. A mechanical vibratory system, an electric circuit, means forcausing the current in said circuit to produce corresponding vibrationsin said system and means for damping said mechanical system, saiddamping means comprising means for producing electrical currentproportional to the vibrations in said mechanical system, means foramplifying and shifting the phase of said produced current and means forimpressing said amplified and phase shifted current upon said circuitwhereby it opposes the action of said first mentioned electrical currenton said mechanical system.

' In witness whereof, we hereunto subscribe our names this 28th day ofDecember, A. D., `1922. i

JOSEPH P. MAXFIELD. HENRY C. HARRISON.

